Strain mapping in nanowires
ABSTRACT A method for obtaining detailed two-dimensional strain maps in nanowires and related nanoscale structures has been developed. The approach relies on a combination of lattice imaging by high-resolution transmission electron microscopy and geometric phase analysis of the resulting micrographs using Fourier transform routines. We demonstrate the method for a germanium nanowire grown epitaxially on Si(111) by obtaining the strain components epsilon(xx), epsilon(yy), epsilon(xy), the mean dilatation, and the rotation of the lattice planes. The resulting strain maps are demonstrated to allow detailed evaluation of the strains and loading on nanowires.
- SourceAvailable from: C. G. Garay-Reyes
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- "By using GPA, the variation in the local lattice constant in the HRTEM micrographs is calculated by taking a strain free area as a reference . Despite its limitation of a relatively small field of view, the method has been used successfully to quantify strain fields around dislocations , Ge nanowires  and more recently on Al–Pb interfaces . Because elastic strain values, caused by GP precipitates, are still controversial in the literature , this work presents a quantitative comparison of the results obtained by the DFH and HRTEM-GP techniques. "
ABSTRACT: Elastic strains, caused by GP zones in an aged Al alloy, were determined quantitatively using two techniques: Dark Field In-line Holography (DFH) and High Resolution Transmission Electron Microscopy-Geometric Phase Analysis (HRTEM-GPA). The results obtained by both techniques showed that the elastic strain was not uniform along the precipitate–matrix interface. In some areas, it was found that strain had negligible value and this was attributed to the loss of coherence between the lattices. It is suggested that a possible explanation for this fact could be a variation in the “vacancies pump mechanism” kinetics. To obtain a better interpretation of the experimental deformation maps, a reference GP precipitate–matrix structure was built using QSTEM software. The main advantages of DFH over HRTEM-GPA were a bigger field of view and low electron dose requirements without spatial resolution loss. Another difference found was that crystalline defects such as dislocations were evidenced by HRTEM-GPA in contrast to the result obtained by DFH. However, strain measurements were affected by mask size effect in the former.Materials Characterization 11/2012; 73:61–67. DOI:10.1016/j.matchar.2012.07.017 · 1.93 Impact Factor
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- "Recently, high-resolution transmission electron microscopy (HRTEM) has become a powerful tool for mapping the deformation field at the nanoscale level because of the development of quantitative image analysis methods  . One such technique is geometric phase analysis (GPA) , which has been applied to a wide variety of systems, such as quantum dots , nanowires , Si/Ge heterostructures , low-angle grain boundaries , etc. The GPA has also been applied to quantitative measurements of deformation fields of edge dislocation in metal  . "
ABSTRACT: A nanoscale experimental study of micro-crack in silicon was presented by using a combination of high-resolution transmission electron microscopy and geometric phase analysis. The results show that there is an amorphous phase content in the crack body. The width of the amorphous narrow band which exists within the crack body is 2nm approximately. The geometric phase analysis technology was applied to calculate the strain fields of the crack tip. The trend of the experiment strain value ahead of the crack tip is the same with the trend of the isotropic elastic theory strain value.Proceedings of SPIE - The International Society for Optical Engineering 11/2008; DOI:10.1117/12.839015 · 0.20 Impact Factor
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ABSTRACT: Strain mapping using the geometric phase analysis (GPA) technique was applied to Al–GP II (Guinier–Preston) nanoscale precipitates, using both high resolution transmission electron microscopy (HRTEM) micrographs as well as the exit wave function (EWF) obtained by focal series reconstruction. The experimental strain results were compared with strain maps obtained from an atomic model which consisted of an Al supercell containing a GP II precipitate. It was built as a reference from literature data. The experimental results demonstrate a complex strain distribution and larger fluctuations than the reference strain maps. These differences were found to be partly a consequence of image artifacts produced by the technique as well as complex microstructural events which were present at the development stage studied.Journal of Alloys and Compounds 09/2012; 536:S159–S164. DOI:10.1016/j.jallcom.2012.01.016 · 2.73 Impact Factor